Ability of solar collector apparatus to work at higher temperatures is advantageous for home spacing heating and other applications. The cost of flat plate solar collectors and their inability to efficiently deliver water at high temperatures in the range of 140.degree. F. to 200.degree. F. usually make them unsuitable for home space heating. Conventional parabolic tracking reflectors can deliver water at high temperatures but are costly.
It is known to use aluminum foil or aluminized mylar foil in parabolic reflectors, but heretofore difficulty in accurately maintaining the parabolic shape of such thin films has reduced their efficiency or rendered their use impractical.
The basic objective is to form the foil into a parabolic cylinder mirror whose line of focus is on a receiver tube. To achieve low cost it is important that the length of the parabolic cylinder that can be accurately formed and maintained be maximized. One difficulty with the prior art parabolic foil collectors stems from the fact that the thin foil itself is unable to support bending moments. The structural beam formed by the parabolic foil cylinder is also unable to support torque along its axis. Bending moments or torque cause the structural beam to deform, displacing the line of focus and degrading the quality of the focus. Hence, it has been impractical to form parabolic flexible foil collectors of sufficient length and durability to achieve the cost effectiveness which is desired from the use of thin foil.
A patent to Cohen, U.S. Pat. No. 4,184,482, describes one proposal for the utilization of a thin sheet for the solar energy reflecting surface. An attempt is made in Cohen to utilize the receiver tube to support the foil collector. However, as in other attempts in the art, little or no provision was made for the prevention of distortion from torque or bending moments. Because of the likelihood of such forces, either the receiver tube or the parabolic cylinder of the Cohen device would soon deform and, hence, that solution is deemed unsatisfactory.
Various other examples of parabolic reflector apparatus and methods of making the same can be found in prior patents as follows:
U.S. Pat. No. 3,635,547--Jan. 18, 1972 PA1 U.S. Pat. No. 3,781,095--Dec. 25, 1973 PA1 U.S. Pat. No. 3,843,238--Oct. 22, 1974 PA1 U.S. Pat. No. 3,973,834--Aug. 10, 1976 PA1 U.S. Pat. No. 4,103,672--Aug. 1, 1978 PA1 U.S. Pat. No. 4,127,926--Dec. 5, 1978 PA1 U.S. Pat. No. 4,173,397--Nov. 6, 1979 PA1 U.S. Pat. No. 4,276,893--Apr. 28, 1981 PA1 U.S. Pat. No. 4,268,332--May 19, 1981